The invention relates to a plunger press and to a method 15.
The plunger press of U.S. Pat. No. 4,034,543 A is an example of prior art and contains a one piece plunger structure, the active compression surface of which corresponds to the cross-section area of the bale case or the material strand in the bale case. The plunger structure compresses during each compression cycle a material charge against the end surface of the material strand. The material charge is fed laterally from the material feeding duct into the bale case while the plunger structure is retracted and against the end surface of the material strand. The plunger structure is coupled via two crank rods to a crank shaft driven via a clutch from a drive source including a fly wheel. The material charge is fed into the bale case by a pivotable feeding fork such that the material charge already is pre-compressed between the plunger structure and the material strand. Each compression cycle is carried out by the entire compression surface of the plunger structure against the material strand on the entire cross-sectional area of the material strand. After each compression cycle, provided that a predetermined compression degree has been reached, the material strand is shifted further by the plunger structure by a step until after several compression cycles the material strand has reached the predetermined length of a bale which is compressed and then is tied by a tying mechanism and is expelled out of the bale case.
The plunger press of U.S. Pat. No. 4,142,746 A has a one piece plunger structure the compression surface of which corresponds to the entire cross-section area of the material strand. As soon as the compressed material strand has reached its desired length the compressed bale is tied into several loops of a twine material by a dual knot type mechanism.
Baled forage, straw, biomass or fibrous mass for agricultural or industrial use when compressed and tied into a compressed bale is transported over long distances. For efficiency reasons a high bale density or degree of compression of the bale is desirable. To achieve sufficient density in a plunger press having a one piece plunger structure requires extremely high plunger forces and considerable primary energy input. Doubling the density of a bale e.g. requires far more than doubling the plunger structure actuation pressure. Therefore, the plunger structure actuation force and the required primary energy will increase massively. However, the efficiency of the power input of e.g. an open channel baler plunger press is not efficient anyhow because in this type of baler not only is energy needed for compressing the material, but also for stepwise shifting the material strand after fed in material is compressed. The energy input for shifting the material strand does not increase the compression so as a matter of fact means a loss for the baling process. Increasing the bale density not only requires a massive increase of the strength of the design of the drive line, the plunger structure and the bale case with its carrying frame, but also requires to undesirably increase the weight of the plunger press. If a fly wheel is used for energy storage, the fly wheel needs to be massive and heavy. Further, e.g. as in the case of a single knot typing mechanism the binding material has to be pulled through the material strand while the material strand is shifting, the twine material pulling force increases drastically if the plunger structure actuation force is increased. This results in undesirably high twine material stress and an acute danger of twining material breakages.